var _curry2 = require('./internal/_curry2');
var _isFunction = require('./internal/_isFunction');
var curryN = require('./curryN');
var toString = require('./toString');


/**
 * Turns a named method with a specified arity into a function that can be
 * called directly supplied with arguments and a target object.
 *
 * The returned function is curried and accepts `arity + 1` parameters where
 * the final parameter is the target object.
 *
 * @func
 * @memberOf R
 * @since v0.1.0
 * @category Function
 * @sig Number -> String -> (a -> b -> ... -> n -> Object -> *)
 * @param {Number} arity Number of arguments the returned function should take
 *        before the target object.
 * @param {String} method Name of the method to call.
 * @return {Function} A new curried function.
 * @see R.construct
 * @example
 *
 *      var sliceFrom = R.invoker(1, 'slice');
 *      sliceFrom(6, 'abcdefghijklm'); //=> 'ghijklm'
 *      var sliceFrom6 = R.invoker(2, 'slice')(6);
 *      sliceFrom6(8, 'abcdefghijklm'); //=> 'gh'
 * @symb R.invoker(0, 'method')(o) = o['method']()
 * @symb R.invoker(1, 'method')(a, o) = o['method'](a)
 * @symb R.invoker(2, 'method')(a, b, o) = o['method'](a, b)
 */
module.exports = _curry2(function invoker(arity, method) {
  return curryN(arity + 1, function() {
    var target = arguments[arity];
    if (target != null && _isFunction(target[method])) {
      return target[method].apply(target, Array.prototype.slice.call(arguments, 0, arity));
    }
    throw new TypeError(toString(target) + ' does not have a method named "' + method + '"');
  });
});